A Composite Analytical Solution for Large-Break LOCA

Abstract

The Canadian CANDU Industry is implementing a composite analytical solution to demonstrate, with high confidence, appropriate safety margins for large-break loss-of-coolant accident (LBLOCA) events in existing CANDU reactors. The methodology involves consolidating several individual approaches in a manner that alleviates reliance on any single analytical method or activity. Using a multi-layered approach, the objective of the composite solution is to use a variety of reinforcing analytical approaches such that they complement one another to collectively form a robust solution.This composite analytical approach enables better risk prioritization, greater physical understanding, and focus for LBLOCA events, and more scrutable, realistic and detailed review while still preserving, and indeed improving, operational safety.

The composite analytical approach (CAA) has undergone refinement to align with Canadian regulatory requirements and expectations for deterministic safety analysis. The CAA involves:

• the threshold break size for systematic reclassification of LBLOCA to beyond design-basis events based on the frequency of the initiating event;
• application of best-estimate and uncertainty analysis methodology to provide a more realistic representation of safety margins;
• continued application of limit of operating envelope methodology to demonstrate the adequacy of margins at the extremes of the operating envelope;
• characterizing the coolant void reactivity, with associated uncertainties; and
• defining acceptance criteria, accounting for the available experimental database and uncertainties.

Bruce Power has undertaken the lead in the implementation of CAA. This paper updates the paper of the same title, presented at the 2011 International Conference on the Future of Heavy-Water Reactors.